Here's an excerise I have done several times that gets people involved - introduce the exercise with a discussion about how the job of a BA is to explore complex situations and problems, analyse the answers and explain them back to users, change management and IT professionals so a solution that meets user requirements and it is unambiguous enough for change mangers and IT professionals to develop a physical solutions.
Now break them up in to groups of 3 or 4 people.
They have to use the following text so give them handouts of the following:
"The names, not necessarily respectively, of the brakeman, fireman, and engineer of a certain train were Smith, Jones, and Robinson. Three passengers on the train happened to have the same names and, in order to distinguish them from the railway employees, will be referred to hereafter as Mr. Smith, Mr. Jones, and Mr. Robinson. Mr. Robinson lived in Manchester; the brakeman lived halfway between Lancaster and Manchester; Mr. Jones earned exactly $20,000 per year; Smith beat the fireman at darts; the brakeman's next-door neighbour, one of the passengers, earned exactly three times as much as the brakeman; and the passenger who lived in Lancaster had the same name as the brakeman.
Each team has to provide a diagramatic and/or textural proof that the engineer must have been called Smith.
Deliverables: flipchart presentation that proves the solution is correct.
Time: 1 hour "
The exercise will require them to find a way of representing the facts that are presented in the text, and deduce new facts from those facts to the point where the inevitable conclusion is that the engineer is called Smith.
If you want to make it really fun and the group dynamics support it, then tell them that they won't be presenting their own answers back to the group but one of the other teams will. I.e. they have to present back each other's answers. This is a really good way of showing that if it is not obviously written down in a logical ordered way it will not communicate.
I have a couple of example asnwers - email me at Guy@smart-BA.com if you want them.
I have seen all kinds of solution to this - most groups succeed but may need helpful hints along the way. The single most common mistake is that they don't write everything down and do not indicate the sequence in which the facts must be uncovered.
Hope this helps and have fun!